Meter reading has been, in the past, a time consuming and expensive task and is particularly difficult in areas where inclement weather, heavy snowfalls, and remote locations prevent meter reading altogether. In these cases they generally estimate the customer usage and bill them accordingly until such time as weather permits actual reading. To solve these problems, systems which use existing telephone lines to provide automatic remote meter reading have been designed. In one such system a switch is opened and closed as the dial on the meter rotates changing DC resistance across the phone line from one value to another and back again. This draws a current on the telephone line which is measured at a central location by monitoring the resulting voltage across the line relay coil. The voltage across the line relay coil is an indicator of the state of the resistor network in the meters connected to the line. Further the state of the resistor network, in turn, is an indicator of the position of the meter dial.
As the resistance switches back and forth between two values a computer at the central location records or stores the consumption for that customer in the computer's memory. The computer at the central location selects the line, scans the network by measuring the current in the line and hence determines the position of the meter dial on that line. In this system the scan cycle repeats frequently, usually every minute taking many more readings than are necessary to detect the encoder state changes which occur over periods of several hours, days or even weeks. Recordings or readings taken during transitions such as telephone in use, ringing or unstable signals on the line are rejected. In this system these signals therefore create interference with the monitoring of utility meters.